A resin substrate is conventionally used as an insulation layer of a substrate. The resin substrate is formed by soaking a cloth of crisscross woven fiber bundles, in a resin and hardening the cloth. When a signal wire is disposed extending over both an area on glass fiber bundles and an area on the resin, the impedance of the signal wire can be varied depending on position due to the difference in the dielectric constant between the fiber bundle and the resin.
Thus, according to one technology, when the fiber bundles are present at a position conforming to the specification in the insulation layer, the wire position of a signal wire is determined such that the signal wire is disposed in an area on the fiber bundles (see, e.g., Japanese Laid-Open Patent Publication No. 2011-82271).
According to another technology, the fiber bundles in the insulation layer are colored; when the substrate is manufactured, a portion of copper foil to be a wiring layer stacked on the insulation layer is peeled and the colored fiber bundles are recognized; thereby, the position of the fiber bundles in the insulation layer is identified; and the wire position of the signal wire is changed such that the signal wire is disposed in the area on the fiber bundles identified (see, e.g., Japanese Laid-Open Patent Publication No. 2011-210839).
Among related technologies is a technology of determining the length and the shape of a signal wire to suppress impedance variations caused by the difference in the dielectric constant between the fiber bundles and the resin (see, e.g., Japanese Laid-Open Patent Publication No. 2009-164416).
However, according to the conventional technologies, disposal of the signal wire in the area on the fiber bundles may not be possible when difference in the position of the fiber bundles in the insulation layer arise consequent to manufacturing tolerances for the insulation layer. Thus, the signal wire may be disposed extending over both the area on the fiber bundles and the area on the resin, and the impedance of the signal wire vary depending on the position. Therefore, the insertion loss of the signal wire may increase.